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- All Subjects: Erosion
- Creators: Chandler, Douglas
- Creators: Christensen, Philip
Description
Some cyanobacteria, referred to as boring or euendolithic, are capable of excavating tunnels into calcareous substrates, both mineral and biogenic. The erosive activity of these cyanobacteria results in the destruction of coastal limestones and dead corals, the reworking of carbonate sands, and the cementation of microbialites. They thus link the biological and mineral parts of the global carbon cycle directly. They are also relevant for marine aquaculture as pests of mollusk populations. In spite of their importance, the mechanism by which these cyanobacteria bore remains unknown. In fact, boring by phototrophs is geochemically paradoxical, in that they should promote precipitation of carbonates, not dissolution. To approach this paradox experimentally, I developed an empirical model based on a newly isolated euendolith, which I characterized physiologically, ultrastructurally and phylogenetically (Mastigocoleus testarum BC008); it bores on pure calcite in the laboratory under controlled conditions. Mechanistic hypotheses suggesting the aid of accompanying heterotrophic bacteria, or the spatial/temporal separation of photosynthesis and boring could be readily rejected. Real-time Ca2+ mapping by laser scanning confocal microscopy of boring BC008 cells showed that boring resulted in undersaturation at the boring front and supersaturation in and around boreholes. This is consistent with a process of uptake of Ca2+ from the boring front, trans-cellular mobilization, and extrusion at the distal end of the filaments (borehole entrance). Ca2+ disequilibrium could be inhibited by ceasing illumination, preventing ATP generation, and, more specifically, by blocking P-type Ca2+ ATPase transporters. This demonstrates that BC008 bores by promoting calcite dissolution locally at the boring front through Ca2+ uptake, an unprecedented capacity among living organisms. Parallel studies using mixed microbial assemblages of euendoliths boring into Caribbean, Mediterranean, North and South Pacific marine carbonates, demonstrate that the mechanism operating in BC008 is widespread, but perhaps not universal.
ContributorsRamírez-Reinat, Edgardo L (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Chandler, Douglas (Committee member) / Farmer, Jack (Committee member) / Neuer, Susanne (Committee member) / Arizona State University (Publisher)
Created2010
Description
Mountain landscapes reflect competition between tectonic processes acting to build topography and erosive processes acting to wear it down. In temperate mountain landscapes, bedrock rivers are the primary erosional agent, setting both the pace of landscape evolution and form of the surrounding topography. Theory predicts that river steepness is sensitive to climatic, tectonic, and lithologic factors, which dictate the rates and mechanics of erosional processes. Thus, encoded into topography is an archive of information about forces driving landscape evolution. Decoding this archive, however, is fraught and climate presents a particularly challenging conundrum: despite decades of research describing theoretically how climate should affect topography, unambiguous natural examples from tectonically active landscapes where variations in climate demonstrably influence topography are elusive. In this dissertation, I first present a theoretical framework describing how the spatially varied nature of orographic rainfall patterns, which are ubiquitous features of mountain climates, complicate expectations about how climate should influence river steepness and erosion. I then apply some of these ideas to the northern-central Andes. By analyzing river profiles spanning more than 1500 km across Peru and Bolivia, I show that the regional orographic rainfall pattern this landscape experiences systematically influences fluvial erosional efficiency and thus topography. I also show how common simplifying assumptions built into conventional topographic analysis techniques may introduce biases that undermine detection of climatic signatures in landscapes where climate, tectonics, and lithology all covary – a common condition in mountain landscapes where these techniques are often used. I continue by coupling this analysis with published erosion rates and a new dataset of 25 cosmogenic 10Be catchment average erosion rates. Once the influence of climate is accounted for, functional relationships emerge among channel steepness, erosion rate, and lithology. I then use these functional relationships to produce a calibrated erosion rate map that spans over 300 km of the southern Peruvian Andes. These results demonstrate that accounting for the effects of climate significantly enhances the ability to decode channel steepness patterns. Along with this comes the potential to better understand rates and patterns of tectonic processes, and identify seismic hazards associated with tectonic activity using topography.
ContributorsLeonard, Joel Scott (Author) / Whipple, Kelin (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Christensen, Philip (Committee member) / Forte, Adam (Committee member) / Heimsath, Arjun (Committee member) / Hodges, Kip (Committee member) / Arizona State University (Publisher)
Created2022